Titanium metal production process



United States Patent Ofifice I 3,012,878 TITANIUM METAL PRODUCTIONPROCESS Werner C. Muller, Roslyn, N.Y., assignor to National Distillersand Chemical Corporation, New York, N.Y., a corporation of Virginia NoDrawing. Filed Sept. 16, 1958, Ser. No. 761,301

Claims. (Cl. 75-8 4.5)

This invention relates to a new and improved process for the productionof titanium metal. More particularly, the invention pertains to acontinuous method for preparing titanium metal.

In recent years numerous processes have been proposed for thepreparation of titanium metal utilizing titanium halides as the startingmaterial. These processes have involved, in general, the reaction oftitanium tetrahalides, especially titanium tetrachloride, with alkalimetal or alkaline earth metal reductants. Though many variations of thisreduction step have been suggested in the prior art, the processesinvariably treat the products obtained from reduction in a separatesintering or fusion step. This treatment involves heating the productmixture of the reduction step to temperatures above the melting point ofthe by-product salts under an inert gas atomsphere or under vacuum.ranged from 800 to 1500 C., though temperatures above 1000 C. have beendiscouraged since special equipment must be employed to avoid alloyingof the titanium with the Walls of the reaction vessels.

The sintering or fusion step appears to serve two purposes: (1) theagglomeration of the titanium particles in the mixture being treatedtoform relatively large chunks of titanium sponge; and (2) the meltingorvaporization of the by-product salts, which facilitates their separationfrom the desired titanium metal. In actual operations, however, the heattreatment of the reaction product mixture obtained from the reductionstep has led to,several serious problems. For one thing, the largechunks of titanium metal sponge which are formed are quite difficult toremove from the reaction vessels. In fact, it has been necessary toemploy air hammers or other similar devices in order to accomplish this.With respect to separation of the by-product salts, it has been foundthat, though a major portion of the salt is removed from the titaniumsponge, some of the salt becomes trapped or encased in the titaniumsponge. Since the removal of this residual salt is essential in order toprepare high quality titanium metal, elaborate procedures have beendevised for this purpose. It is obvious that the special equipment andprocess steps required to recover and treat the titanium sponge obtainedfrom the sintering or fusion step are costly and time consuming incommercial operations. Moreover, additional processing steps areundesirable from the standpoint of possibly introducing contaminantsinto the titanium sponge at an advanced stage of the process. I

It is one object of this invention to provide a titanium manufacturingprocess which avoids the difiiculties encountered in the prior artprocesses. Another object of the invention is to provide acontinuousmethod'which readily permits control over the size of thetitanium sponge produced. A further object is to provide a processSpecific temperatures employed have- Patented Dec. 12, 1961 point of thereaction product mixture, i.'e. 'a mixture of the titaniui'nmetalproduct and the alkali'metal halide by-product, -More specifically, thereaction temperature will be within the range of about 400 r0700" C.,preferably about 500 to 600 C. Thus, for example, when titanium metaland sodium chloride are obtained as the reaction products in accordancewith the preferred eml vention is started up the reaction mediumconstitutes the reaction product mixture. v As set forth below, vari ousmethods and equipment may be employed in carrying out this particularstep of the process for maintaining the desired amount of reaction mediain the reaction zone and for recovering the titanium metal product.

In general, the reduction step comprises metering 'controlled amounts ofthe titanium subhalidealkali metal complex mixture and the alkali metalreductant into the reaction zone-containing the particulatetitanium andthe finely divided,s olid alkali metal halide, which is maintainedundervlconstantagitation. The amount of re actants added to the reactionbed is preferably sufiicient to ensure substantiallystoichiometricreductionof the titanium subhalide alka'li metal complexmixture, al-

' 'though a slight excess or deficiency'of the alkali metal that hascommercial application and produces high quality titanium metal.

In accordance with the present invention, these and may be utilizedwithout deleterious results. The reactants may either be fedcontinuously or intermittently into the reaction zone. v Itis'important, however, 'to con: trol the amount of reactants addedso'that a large excess of the reaction medium is alwayspresent. Inactual operations it is advisable to maintain the weight percentage oftotal reactants below about 10%, preferably within the range of about 3to 7% by weight, based on the weight of the reaction medium, thoughhigher percentages up to about 25% may be employed. i

The alkali rnetal redu'ctant and; the titanium subhalide-. alkali metalhalide complex may be added to the reaction zone either in solid or inmolten'form. For the purposes of easier handling, the alkali metal willbe moltenv while the titanium subhalide-alkali metal halide will befinely divided solids.

Conventional equipment may be employed for carry-.

ing out the reduction reaction. In order to avoid contaminating thetitanium metal product, it is preferred to operate in a closed system orunder an; inert gas atmosphere such as argon, helium, neon and the like.Since it is an important feature .of this invention to maintain thereaction mixture, including the reaction medium, in a constant state ofagitation, the reaction 'vessel' mustbe provided with a mixing. device'or be capable of being rotated in such a'man'ner that its contents willbe'subjected to the desired degree of agitation- The mixing equipmentcan be either paddles, tumbling barrels, ball mills and thevlike. Itwill be'further understood that the stirring will be sufiiciently slow.enough to avoid the disintegration of the titanium metal particles=-thatare formed during the course of the reaction. 4

In accordance with one method of carrying-out the; process of thisinvention, the titanium subhalide-alkali metal halide complex mixture.and the alkali metal reductant are fed viaseparate gravimetric feedersand lines into the upper portion of a closed reaction vessel equippedwith a blade type of stirrer and containing a reaction medium comprisingparticulate titaniummetal and finely divided, solid alkali metal halidehaving an average particle size of less than about mesh. The stirrer isrotated at a speed sufficient to effect constant agitation of thereaction mixture. The reaction mixture is maintained at a temperaturewithin the range of about 400 to 700 C. The reaction between thetitanium subhalide-alkali metal halide complex mixture and the alkalimetal results in the formation of titanium metal and alkali metal halideby-product. Though the exact nature of reaction mechanism is notunderstood, it is believed that the titanium subhalide-alkali metalhalide complex mixture, molten under the aforementioned operatingconditions, deposits in layers on the particulate titanium metal and thefinely divided, solid alkali metal halide in the reaction medium. Uponreaction with the alkali metal, granular particles of the titanium metalmixed with by-product alkali metal halide are formed. The processcomprises coating a layer of the molten titanium subhalidealkali metalhalide on the particulated or granular solids in the reaction mixturefollowed by reaction with the alkali metal to form larger granules orporous particles comprising the titanium metal mixed with the alkalimetal halide by-product continuously until the granules are recoveredfrom the reaction zone or become so heavy that they fall to the bottomof the reaction zone. Preferably, a portion of the reaction productmixture is removed either continuously or at intervals from the reactionzone. The portion of the reaction product mixture so recovered is thenscreened or otherwise classified to separate the desired titanium spongeparticles from the more finely divided particles, including theparticulated titanium metal and finely divided alkali metal halide uponwhich no titanium metal has been deposited. These finely dividedparticles may be recycled to the reaction zone to act as the reactionmedium. If additional reaction medium is required to maintain bedvolume, some of the larger particles recovered from the reaction zonemay be crushed or ground to obtain the desired particle size and thenrecycled to the reaction zone.

The granulated titanium-alkali metal halide particles recovered from thereaction zone and having the desired particle size are Washed or leachedwith water, mineral acids or mixtures thereof to remove the alkali metalhalide salt therefrom. Mineral acids such as hydrochloric, sulfuric,etc. may be employed for this purpose. Following the leaching step ofthe present process, the titanium metal product is dried by conventionalmeans. The dried titanium metal product is characterized asbeingsponge-like, and it has numerous commercial applications known tothe art.

Another method of carrying out the method of this invention is to feed,continuously or intermittently, the titanium subhalide-alkali metalhalide complex and the alkali metal separately to the front end of aribbon mixer containing a bed of particulate titanium metal and finelydivided, solid alkali metal halide. Other than the difference inequipment, all of the operating conditions will be the same aspreviously described. A portion of the reaction products in admixturewith the reaction medium is continuously withdrawn from the reactionvessel. In accordance with the preferred method of the invention, someof the withdrawn mixture is recycled back to the front end of the ribbonmixer. As discussed above, the material to be recycled may be crushed orground prior to being passed to the vessel in order to obtain theparticle size required for proper functioning as the reaction medium.The titanium metal granules having the desired particle size aresequentially leached and dried to recover the titanium metal product.

The alkali metal reductant useful in the present process includessodium, potassium and lithium. Sodium is the preferred reducing agent.As previously set forth, the amount of alkali metal employed in thereduction will be sufiicient to ensure stoichiometric reduction of the 4titanium subhalides in the feed material to the titanium metal.

The titanium subhalide-alkali metal halide complex mixture employed asthe feed material may be obtained in accordance with the processesdescribed in United States Patent No. 2,765,270 issued to Brenner et al.on October 2, 1956. .As is noted in this patent, the exact nature of thematerial has not been determined. For the sake of uniformity ofnomenclature, therefore, the material will be referred to as a chemicalcomposition or a complex, which conforms to the following empiricalformula:

in which M is an alkali metal such as sodium, potassium, lithium, etc.and X is a halide such as chlorine, bromine and iodine. The ratio of ato b to 0 will be l3:l:4. In the preferred feed material, M is sodiumand X is chlorine. It will be understood that the titaniumsubhalidealkali metal halide complex may be prepared by methods otherthan those described in Brenner et al., and that, furthermore, the exactmethod of producing this material does not constitute an essentialfeature of this invention. One important advantage of the inventiveprocess is that the heat transfer problems encountered instoichiornetrically reducing the titanium tetrahalides to the metal in aone-step operation are avoided. If, for example, the titaniumsubhalide-sodium halide complex is formed by the reaction of titaniumtetrahalide with'a controlled deficiency of sodium, such as about 50% ofthe stoichiometric amount, more than half of the total exothermic heatof reaction involved in stoichiometric reduction is released at thisstage. By operating inthis manner run-away temperatures and theformation of hot spots are prevented, and the heat released during thesubsequent reaction of the titanium subhalide-sodium halide complex withsodium, as carried out in accordance with the invention method, isadvantageously utilized to prepare the desired titanium metal product.

The invention will be more fully understood by reference to thefollowing illustrative examples.

Example I A titanium subchloride-sodium chloride complex, conforming tothe empirical formula Na TiCl is fed into a sealed reaction vesselequipped with a blade stirrer. The reaction vessel is about threequarters full of a solid, particulated reaction medium comprisingtitanium particles and sodium chloride. Molten sodium is also fed intothe reaction vessel at a rate sufficient to ensure the completereduction of the complex to form titanium metal and by-product sodiumchloride. The resulting reaction mixture is maintained under an argonatmosphere and is subjected to constant agitation by rotating thestirrer at a rate of about 50 rpm. The reaction is carried out at atemperature of about 590 C., which is above the melting point of thefeed mixture but below the melt-. ing point of sodium chloride andtitanium. The titanium subchloride-sodium chloride complex, molten underthe reaction conditions becomes coated on the discrete particles of thereaction medium and reacts with the molten sodium to form sponge-likeporous titanium metal in admixture with sodium chloride. The quantity ofthe reaction mixture is maintained substantially constant bycontinuously withdrawing a portion of the reaction mixture. The materialwithdrawn is filtered through a 40 mesh screen. The particulatedmaterial, which passes through the screen, is recycled to the reactionvessel. The granulated particles retained on the screen are passed to aconveyor where they are countercurrently washed with water and HCl toremove the by-product sodium chloride. The granulated titanium metalsponge recov ered is substantially free of sodium chloride.

Example II A feed material comprising titanium subchloride-sodiumchloride complex, having the empirical formula Na TiCl is intermixed ina ribbon mixer with particulated titanium metal and finely divided solidsodium chloride. The feed line for the complex material is positioned atthe top of the ribbon mixer and at a point near the front end. Sodium isalso fed continuously into the mixer via a line positioned at a pointremoved from the feed line for the complex feed material but in thedirection in which the reaction mixture is moving with agitation. Thefeed lines of the reactants are so positioned that the titaniumsubchloride-sodium chloride which becomes molten under the operatingconditions (i.e. a temperature of about 550 C.) is coated on theparticulate reaction medium, and then reacts with the sodium added tothe mixture to form granules of porous titanium metal in admixture withby-product sodium chloride. The resulting reaction product mixture andthat portion of the reaction medium which is left unchanged is recoveredfrom the discharge end of the ribbon mixer. The recovered material isscreened to separate the titanium granules formed during the reactionfrom the particulate titanium metal and sodium chloride. The lattermaterial is recycled to the feed end of the ribbon mixer at a pointlocated in front of the titanium subchloridesodium chloride complex feedline. The separated titanium metal granules are then leached and driedin the same manner described in Example I. The titanium metal recoveredis sponge-like and is substantially free of by-product sodium chloride.

The foregoing embodiments describe only two possible ways of operatingthe process of this invention. It will also be understood that thesemethods may be modified Without departing from the broader aspects ofthe invention. The essential features of the invention include the useof a titanium subhalide-alkali metal halide complex feed material and areaction medium comprising a mixture of solid, particulated titaniummetal and alkali metal halide. Important operating conditions arereaction temperatures above the melting point of the complex feedmaterial but below the melting point of the alkali metal halide, andconstant agitation of the reaction mixture. As shown above, the processof this invention readily permits control over the size of the titaniummetal particles which can be produced. Thus, for example, largesponge-like titanium particles can be obtained by utilizing one or moreof the following procedures: (1) retaining the reaction mixture in thereaction vessel for a longer period of time, (2) recycling 3. majorportion of the reaction product mixture to the reaction zone and (3)separating only the largest titanium particles from the reaction productmixture and recycling the remaining product material, includingunchanged reaction medium, back to the reaction zone. Granulatedtitanium metal particles within the range of about to 100 mesh,preferably about 20 to 80 mesh, can be achieved in the inventiveprocess.

As previously described, once the process is on stream, the reactionmedium comprising particulate titanium metal and solid, finely dividedsodium chloride may be maintained at the desired volume by recycling theunchanged material withdrawn along the granulated titanium product.Additional reaction medium can be supplied by grinding or crushingportions of the titanium granules or by utilizing the product mixtureobtained from the stoichiometric reduction of titanium tetrahalides withalkali metal.

The titanium metal product obtained in accordance with the process ofthis invention has a number of distinct advantages. Since the elevatedsintering temperatures employed in the prior art process have beenavoided, the removal of by-product alkali metal halide is simplified.Moreover, the titanium product is of high quality and can be employed invarious processes calling for formula M {ii X wherein M is an alkalimetal, X is a halide and the ratio of a to b to c is 1-3: 1:4, to alarge excess of an agitated mixture comprising solid, finely dividedtitanium metal particles and an alkali metal halide at a temperatureabove the melting point of said material but below the melting point ofsaid alkali metal halide and within the range of about 400 to 700 C.whereby said material coats a portion of said agitated mixture; addingan alkali metal to said partially coated mixture while continuingagitation, said alkali metal being in an amount Suthcient to react withsaid material, the weight percentage of said reactants being maintainedbelow about 25% based on the weight of said agitated mixture, to formtitanium metal sponge at said temperature; recovering the resultingreaction product mixture; and separating therefrom the titanium metalsponge.

2. The process of claim 1 wherein the material has an empirical formulaof Na TiCl 3. The process of claim 1 wherein said alkali metal reactantis sodium.

4. The process of claim 1 wherein the reaction product mixture,following removal of the titanium metal sponge, is recycled to saidagitated mixture.

5. The process of claim 1 wherein said reaction is carried out in aninert atmosphere.

6. The process of claim 1 wherein said titanium metal sponge has aparticle size greater than said finely divided titanium metal. a

7. A continuous process for preparing granulated titanium metal whichcomprises the following steps: (1) agitating a mixture comprising solid,finely divided titanium particles and sodium chloride in a reaction zoneat a temperature of above about 400 C. but below about 805 C., (2)adding titanium subchloride-sodium chloride complex to said agitatedmixture whereby said complex coats a portion of said agitated mixture;(3) adding sodium to said agitated coated mixture while continuingagitation to effect reaction at said temperature with said titaniumsubchloride-sodium chloride complex to form titanium metal in admixturewith sodium chloride, the weight percentage of said reactantsbeing'maintained below about 25% based on the weight of said agitatedmixture; (4) repeating steps (2) and (3) in a continuous manner untillarge titanium granules are formed; (5) continuously removing a portionof the resulting reaction product mixture from the reaction zone; (6)separating the titanium granules from the reaction product mixture.

8. The process of claim 7 wherein said temperature is about 500 to 600C.

9. The process of claim 7 wherein said complex has an empirical formulaNa TiCl 10. The process of claim 7 wherein a portion of the recoveredreaction product mixture is recycled to the reaction zone.

References Cited in the file of this patent UNITED STATES PATENTS2,765,270 Brenner et al. Oct. 2, 1956 2,816,021 Quin Dec. 10, 19572,824,799 Hansley et al. Feb. 25, 1958 2,827,371 Quin Mar. 18, 19582,830,888 Wade Apr. 15, 1958 2,835,568 Kingsbury May 20, 1958 2,882,144Follows et a1. Apr. 14, 1959 2,910,357 Muller Oct. 27, 1959

1. A PROCESS FOR PRODUCING TITANIUM METAL SPONGE WHICH COMPRISES ADDINGA MATERIAL, HAVING THE EMPIRICAL FORMULA